Solvent development of light-sensitive diazo layers

ABSTRACT

The development of positive-working light-sensitive diazo layers for use as lithographic printing plates and photoresists is effected using selectively acting organic solvents to dissolve light-struck areas.

United States Patent DIAZO LAYERS 10 Claims, No Drawings 11.8. CI 96/49,96/33, 96/36, 96/36.2, 96/36.3, 96/1 LY Int. Cl G03f 7/02,

[50] Field of Search 96/48, 49, 33, 36.3, 36

[56] References Cited UNITED STATES PATENTS 3,019,106 H1962 Adams 96/483,406,065 10/1968 Uhlig 96/36.3 FOREIGN PATENTS 844,039 8/1960 GreatBritain 96/36 784,001 10/1959 Great Britain Primary Examiner-Norman G.Torchin Assistant Examiner-John Winkelman Attorney-McClew and TorenABSTRACT: The development of positive-working light-sensitive diazolayers for use as lithographic printing plates and photoresists iseffected using selectively acting organic solvents to dissolvelight-struck areas.

SOLVENT DEVELOPMENT OF LIGHT-SENSITIVE DIAZO LAYERS BACKGROUND OF THEINVENTION Positive-working light-sensitized lithographic plates areknown and disclosed, for example, in U.S. Pat. Ser. Nos. 3,046,121 and3,046,120 and in United Kingdom Pat. Specifications Nos. 739,654 and1,034,191 according to which the sensitized layer comprises adiazo-oxide derivative. Such plates are also disclosed in U.S. Pat. No.3,219,447 where the sensitized layer comprises a mixture of a diazoniumderivative with an alkali-soluble novolak resin. The sensitized layer ineach case may be applied to a metal such as an aluminum or zinc sheet.The image on such plates is developed by the use of alkaline developerswhich are not only unpleasant to handle but may have a corrosive effecton the areas of the plate laid bare by such development. This effect isparticularly marked in the case of plates which have been chemically orelectrochemically grained.

These alkaline developers have the further disadvantage that while thecontents of a stock bottle are being used the alkalinity becomes reduceddue to absorption of carbon dioxide from the air. This becomes veryimportant in developing machines. This development in generally followedby treatment with an acid desensitizer.

The use of grained or anodized printing plates in lithography is wellknown as being desirable (e.g. see L. E. Lawson, Offset Lithography,Vista Books, London 1963). By graining or anodizing we mean theproduction of a finely textured matte surface on a metal printing plateand the work matte as used herein has reference to such treatment.So-called scratch brushed aluminum plates are also on the market. Theseare simple to produce by mechanical means, but do not meet all therequirements of the printer in practice. Grained and/or anodizedprinting plates exhibit an increased water wettability of thenonprinting area as well as permitting a better control over the amountof moisture present when printing. The action of the nonprinting areasis dependent on a desensitizing layer and the roughened surface assistsin retaining this layer. In addition, graining or anodizing allows aconsiderable amount of wear to occur before the desensitized layer isseriously affected and furthermore, it promotes adhesion of thelight-sensitive layer as well as of the final image. Above all, agrained or anodized plate is preferred by the printer for ease of use inthat the balance between ink and water, i.e., the control of thefountain solution, is not so critical.

The application of the positive-working process using matte metalsurfaces has in particular, as well as the possibility of corrosionmentioned above, the disadvantage that on development of the plate withan alkaline developer, the exposure products of the diazo oxides ordiazonium derivatives may form a stain or dye in the nonimage areas withthe possibility of retention of small particles in the pits of the grainof the matte surface, which makes the plate unacceptable to the printerbecause of the risk of ink-acceptance in the nonprinting areas of theplate.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a new process for the development of positive-workinglithographic plates in which the use of an alkaline developer can bedispensed with.

We have now found unexpectedly that the alkaline developer may bedispensed with in the development of positive-working lithographicplates as described above and that one may simply use as developer asolvent for the layer in the nonimage areas, if desired combined with alithographic desensitizer.

By the term positive working as used herein and in the appended claimswe mean not only a positive image produced from a positive transparencybut also positive resist processes where, according to the process, anegative transparency may be needed.

The use of solvent development according to the invention, besides theadvantages mentioned above, also lends itself to the possibility of useof an emulsion of solvent and aqueous desensitizer solution, thus givingone solution processing for the plate, and to the possibility of acombined developer, desensitizer, and reinforcing lacquer. Furthermoreit gives the possibility of use of a tough nonphotosensitive sublayerwhich is solvent soluble and which is removed in the nonimage areas bythe developing agent but remains to reinforce the image areas. The meansof development adopted may be any of those used in the trade such asswabbing, immersion in tank or dish, or use of a developing machine.

According to the invention therefore, we provide a process for thedevelopment of positive-working lithographic plates in which the exposedlithographic plate is treated with a solvent or mixture of solvents forthe presensitized coating selectively to remove the layer from thoseareas which have been exposed, that is from the nonimage areas, thesolvent or solution, if desired, containing a desensitizer.

The fact that is is possible to develop metal positive-working plates bythis process is very surprising and was not to be expected on the basisof existing knowledge of positive-working lithographic plates. There isa previous reference to solvent development using aqueous alcohol oraqueous alcoholic calcium chloride in United Kingdom Pat. SpecificationNo. 732,544, but in that case the image obtained turned out to be anegative copy of the original, as the solvent preferentially dissolvedthe unchanged, diazo-oxide, nonexposed, areas of the layer. The sameresult was obtained by the process of United Kingdom Pat. SpecificationNo. 860,386 where use is made of tetralin combined with a gum-etchdesensitizer. United Kingdom Pat. Specification No. 784,001 describespositive working plates based on diazo-oxides but its method isrestricted to paper plates which have to be specially subbed and wherethe developers are restricted to aliphatic polyhydroxy compoundsfollowed by the use of an alkanolamine to impart a hydrophilic characterto the sublayer.

The actual solvent or solvents used as developer will be selected havingregard to the particular type of positive-working lithographic plate andto the means of development used. This selection can be made by simpleexperiment and presents no difficulty. The selected solvent should beone which dissolves the layer at an appreciable rate in the nonimageareas, that is in exposed areas, while having no substantial effect onthe remaining sensitive layer in the image areas. It should alsopreferably be a solvent which is cheap and commercially available aswell as one which presents no difficulties in use, for example from theodor or toxicity point of view.

Preferred solvents are in general higher boiling organic solvents whichare generally immiscible with water. Suitable classes of solventsinclude in particular aliphatic alcohols and ketones as well as organicesters.

2-ethyl hexanol,

l-octanol,

2,6-dimethyl-4-heptanone, 6-methyl-3'heptanone,

n-hexyl acetate,

diethylphthalate,

diethyl carbonate,

3-methyl-2-pentanone,

Industrial ethyl alcohol.

The solvents used according to the invention may be used in combinationwith desensitizer and if desired a lacquer or similar reinforcing orprotecting agent may also be applied with the solvent so that afterdevelopment an image is obtained in which the nonimage areas have beendesensitized while the image has been coated with a protective lacquer.In adopting this procedure a suitable desensitizer, such as a gumetchbased for example on gum arabic, and phosphoric acid solution may beused combined in suitable proportions, for example lzl by weight withthe selected solvent. An emulsifying agent may be added to this ifdesired. If a reinforcing lacquer is needed to be applied, for example anovolak resin or an epoxy resin, this may also be applied in solution inthe selected developer. Finally it may be found to be advantageous toadd a dye or pigment to the developer to render the image more visible,or to add a photodesensitizing dye to render the image insensitive tolight.

When a lithographic plate is being made the metal used may be selectedfrom a number of possibilities, provided the surface can be renderedhydrophilic after scratch-brushing or preferably after graining and/oranodizing. The plate metal is preferably aluminum or zinc but this isnot essential. When the coating is used as a photoresist many othersubstrates may be employed according to the process being carried outbut the same means of development can be used to give good results withresists for use on e.g. multimetal plates, copper plates or cylinders.In some of these cases, a negative transparency may be needed to give afinal positive printing image. In the case of printed circuit resists, apositive transparency or a negative transparency of the final circuitwill be needed according to the process being used. The developmentprocess of the invention may also be used on electrophotographic orxerographic printing plates where the resin image is formed as a resiston a layer of alkali-soluble material which has to be removed in thenonimage areas, e.g., United Kingdom Pat. Specification Nos. 917,641 and944,126.

The following examples illustrate the invention. In these examples theprinting plates all have a diazo oxide or diazoniumderivative-containing sensitized layer. I

EXAMPLE 1 An Ozasol Aluminum Positive Printing Plate P4 alight-sensitive lithographic plate in which the light sensitive materialis a quinone diazide sulphonic acid ester was exposed under a positivetransparency and developed with 2-ethyl-hexanol as solvent by rubbingwith a swab for minutes; after removing excess solvent, the plate wasrubbed with commercial gumetch solution, rinsed and dried well by meansof hot air, when it was ready to use in a printing machine. Similarsatisfactory results were obtained when l-octanol,2,6-dimethyl-4-heptanone, and diethyl phthalate were used as solvent; inthe case of the last 2 solvents development was faster than withethylhexanol or l-octanol but care had to be taken not to keep the platein contact with the developer after development was complete to avoiddamage to the image area. Similarly 2-ethyl hexanol may be used with anOzasol Positive Printing Plate P6, a light-sensitive lithographic platein which the light sensitive material is a quinone diazide sulphonicacid ester.

EXAMPLE 2 A Ferrania Presensitized Offset Plate, light-sensitivelithographic plates in which the light-sensitive material is a quinonediazide sulphonic acid ester, was exposed under a positive transparency.It behaved in the same way with the solvents given in example 1.

EXAMPLE 3 An Ozasol Chromium on Brass N5 Plate light-sensitivelithographic plates in which the light sensitive material is a quinonediazide sulphonic acid ester, was exposed under a negative transparencyand developed with 2-ethyl hexanol, wiped off, dried, and etched with ahydrochloric acid etch to lay bare the oleophillic metal in the imageareas. The resist was then removed from the chromium areas which arehydrophilic by means of a solvent such as 2-ethoxyethanol.

EXAMPLE 4 The plate of example 1 was developed with a mixture of equalparts of 2-ethyl hexanol and a solution of 30 percent gum arabic, 5percent mono-ammonium phosphate, 5 percent orthophosphoric acid, and0.25 percent Perminal BX (Imperial Chemical Industries Ltd), the sodiumsalt of an alkylated naphthalene sulphonic acid. After rinsing anddrying it was ready for the printing press. The Ozasol Plate P6 behavedsimilarly.

EXAMPLE 5 A solution of 2 percent 4'-methoxy-diphenylamine-4- diazoniumchloride and 10 percent novolak (Pioneer Resin 429-Fredk. Boehm Ltdproduced by condensing formaldehyde with o-cresol) in 2-ethoxyethanolwas coated on to a grained aluminum plate in a plate-whirler and whendry was stoved for 2 minutes at C. After exposure under a screenedpositive transparency it was successfully developed with6-methyl-3-heptanone following the procedure of example 1. Similarly,may be used, 2,6-dimethyl-4-heptanone, lhexyl acetate and diethylcarbonate. When a similar plate was developed with 3 percent trisodiumphosphate solution, a stained background was obtained.

EXAMPLE 6 An exposed plate obtained as in example 5 was developed withthe emulsion developer of example 4 with successful results. Similarresults were obtained with an emulsion of 2,6- dimethyl-4-heptanone inplace of 2-ethyl hexanol.

EXAMPLE 7 A plate prepared and exposed as in example 5 was developedwith an emulsion containing 50 ml. 2,6-dimethyl-4- heptanone and 50 ml.of an aqueous solution of 1 percent sodium metasilicate and 2% percentof the hydrophilic colloid known as Gantrez-half amide (General Anilineand Film Corporation, New York), or Gantrez AN4l4l which is the halfamide of a copolymer of methyl vinyl ether and maleic anhydride to givea satisfactory printing plate.

EXAMPLE 8 0.5 g. of the diazo resin p-toluene sulphonate prepared as inUnited Kingdom Pat. Specification No. 944,276 was dissolved in a mixtureof 5 ml. water and 5 ml. formdimethylamide'and added to 40 ml. of a 10percent solution of novolak in Z-ethoxyethanol. This solution was coatedon to a grained aluminum plate which was stored at 100 for 1 minuteafter it had dried. It was exposed under a positive transparency anddeveloped with 2,6-dimethyl-4-heptanone and then gum etched to give apositive printing plate. in this case, use of an emulsion developer wasunsuccessful.

EXAMPLE 9 2 g. of the bis-[naphthoquinone-( l,2)-diazide-(2)-5-sulphonic acid ester] of 4,4'dihydroxy-diphenyl-sulphone and 2g. PR429(Pioneer-resin 429) novolak were dissolved in a mixture of 50 ml.formdimethylamide and 50 ml. 2-ethoxyethanol and a plate of grained andanodized aluminum was coated with the solution using a whirler. Whendry, the plate was exposed under a positive to the light from acarbon-arc lamp developed with 2-ethyl hexanol, gum-etched and inked into give a printing plate free of stain in nonimage areas.

EXAMPLE 10 The naphthoquinone (l,2)-diazide-(2)5sulphonic acid ester ofnovolak PR429 (see U.K. Pat. Specification No. 711,626) was made up as a2 percent solution in 2-ethoxyethanol and coated on to a grainedaluminum plate. After exposure under a positive it was developed withindustrial alcohol to give a printing plate.

EXAMPLE 1 l A plate coated as in example 5 was exposed under a positiveand developed by means of an emulsion prepared from 20 g. Pioneer Resin,429, l g. Methyl Violet, 60 ml. 2,6-dimethyl-4- heptanone and 60 ml. gumetch. The result was a developed and desensitized lithographic plate,bearing on the image a resin reinforcement to give a longer printingrun.

EXAMPLE 12 A grained aluminum plate was coated at 0.5 g./m. with a sublayer of Vinylite Resin VYHH (Bakelite Ltd., London) a copolymer ofvinyl chloride, from a 5 percent solution in Butoxyl (methoxybutylacetate) and this, after drying, was

coated using the solution of example 5, to give a total coating weightof 4 g./m. After exposure under a positive and development with2,6-dimethyl-4-heptanone, the plate was dried and gum-etched to give aplate which, while having a short exposure time, had a very longprinting life.

EXAMPLE 13 Copper foil laminated to resin impregnated board as used inproduction of printed circuits was coated using the solution of example5, and when dry was heated for 2 minutes at 100. After exposure under apositive pattern of the design of an electronic circuit, the board wasdeveloped with 6-methyl-3- heptanone, dried and the exposed area ofcopper etched away with ferric chloric solution. After this the boardwas rinsed and the resist removed with Z-ethoxyethanol leaving therequired copper circuit.

EXAMPLE 14 The procedure of example 13, was followed except that anegative pattern of the circuit was used. The developed board iselectroplated with silver and after rinsing and removal ofthe resistfrom the nonexposed areas, the copper areas laid bare were removed bymeans of a ferric chloride etch to leave the desired circuit assilver-plated copper.

EXAMPLE IS A plate coated as in example 9 was exposed under a negativetransparency and developed by wiping over with 2-ethylhexanol using aswab of cotton wool. After rinsing with fresh solvent the plate wasthoroughly dried and then etched with the deep-etch solution sold in thetrade as Deep-Etch U- Algraphy Limited, an etch for aluminum which isbased on zinc chloride, for 4 minutes. After rinsing with water anddrying the plate was lacquered in the image areas with a solution of 8percent Epikote 1001 Resin (Shell Ltd.) an epoxy resin) in 60 percentMesitylene, 40 percent Xylene, including 0.5 percent oil-soluble bluedye. After drying the plate was given a fogging exposure with acarbon-arc lamp, the stencil removed with 1 percent sodium hydroxidesolution and the plate gummed up ready for the press.

EXAMPLE 16 A plate coated as in example 5 was exposed under a negativetransparency and developed by wiping over with 2,6- dimethyl-4-heptanoneusing a swab of cotton wool. After rinsing with fresh solvent, the platewas thoroughly dried and then etched with the deep-etch" solution soldin the trade as Deep-Etch UAlgraphy Limited for 4 minutes. After rinsingwith water and drying the plate was lacquered in the image areas eitherwith Patralac, a deep etch lacquer which contains a copolymer of vinylchloride, or with a solution of the Vinylite Resin VYHH (Bakelite Ltd.)10 percent in 2,6- dimethyl-4-heptanone containing 0.5 percentoil-soluble blue dye. After drying the plate was given a foggingexposure with a carbon-arc lamp, the stencil removed with 5 percenttrisodium phosphate solution and the plate gummed up ready for thepress.

We claim:

1. Process for the development of imagewisc exposed photosensitivematerial coated in a layer on a support in admixture with analkali-soluble resin and selected from the group consisting ofdiazo-oxides and diazonium derivatives, which process comprises treatingthe exposed layer with a developer comprising a nonalkaline phasecontaining a waterimmiscible organic solvent for the light-struck areasof the material to selectivelyJ dissolve the light-struck areas of thematerial, said solvent emg selected from the group consisting ofaliphatic alcohols and ketones, and organic esters.

2. Process in accordance with claim 1, wherein the developer includes adesensitizer to render hydrophilic the underlying areas of the supportrevealed on selective removal of the light-struck areas.

3. Process in accordance with claim 1, wherein the developer is in theform of an aqueous emulsion.

4. Process in accordance with claim 1, wherein said organic solvent isselected from the group consisting of 2-ethyl-hexanol; l-octanol;2,6-dimethyl-4-heptanone; 6-methyl-3-heptanone; 3-methyl-2-pentanone;n-hexyl acetate; diethyl phthalate and diethyl carbonate.

5. Process in accordance with claim 1, wherein the developer includes aresin which is deposited on the nonlightstruck areas during development.

6. Process in accordance with claim 5, wherein the resin is selectedfrom the group consisting of novolak resins and epoxy resins.

7. Process in accordance with claim 1, wherein the developer includes amaterial selected from the group consisting of dyes and pigments whichis deposited on the nonlightstruck areas during development to rendersaid areas more visible.

8. A process as claimed in claim 1, wherein the developer includes aphotodesensitizing dye which is deposited on the nonlight-struck areasduring development to render said areas insensitive to light.

9. Process according to claim 1, wherein said support is metal.

10. Process according to claim 1, wherein a tough nonphotosensitivelayer is interposed between the photosensitive material and the support,said nonphotosensitive layer being soluble in the developer.

2. Process in accordance with claim 1, wherein the developer includes adesensitizer to render hydrophilic the underlying areas of the supportrevealed on selective removal of the light-struck areas.
 3. Process inaccordance with claim 1, wherein the developer is in the form of anaqueous emulsion.
 4. Process in accordance with claim 1, wherein saidorganic solvent is selected from the group consisting of2-ethyl-hexanol; 1-octanol; 2,6-dimethyl-4-heptanone;6-methyl-3-heptanone; 3-methyl-2-pentanone; n-hexyl acetate; diethylphthalate and diethyl carbonate.
 5. Process in accordance with claim 1,wherein the developer includes a resin which is deposited on thenonlight-struck areas during development.
 6. Process in accordance withclaim 5, wherein the resin is selected from the group consisting ofnovolak resins and epoxy resins.
 7. Process in accordance with claim 1,wherein the developer includes a material selected from the groupconsisting of dyes and pigments which is deposited on thenonlight-struck areas during development to render said areas morevisible.
 8. A process as claimed in claim 1, wherein the developerincludes a photodesensitizing dye which is deposited on thenonlight-struck areas during development to render said areasinsensitive to light.
 9. Process according to claim 1, wherein saidsupport is metal.
 10. Process according to claim 1, wherein a toughnonphotosensitive layer is interposed between the photosensitivematerial and the support, said nonphotosensitive layer being soluble inthe developer.